• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Box and Driver Measurement

Matthias McCready

Active Member
Joined
Jul 2, 2021
Messages
209
Likes
273
I am attempting to expand my knowledge of loudspeaker measurement and verification, and the scientific processes involved.

At work I have been tasked with going through 7 venues loudspeaker systems, both line-array elements & point source enclosures, and to verify that all of the components are working as they should. Some of these systems are older, and have been pushed hard over the past decades. Previous methods of checking have been simpler, and I think we may have missed problems, so I am wanting to up the ante.

I know SMAART will give me measurements for magnitude, phase, and measurement coherence over frequency; with which data I should be able to verify that:

A) Boxes are generally in phase (it may be hard to verify individual drivers without pulling boxes apart).
B) Drivers are working (If 1 of 2 woofers in a box is not working that should result in a drop in magnitude over the respective frequencies, compared to other boxes of the same model).

---

Additionally I am looking for a way to quantify if drivers are blown or "tired," and I am not sure if this would necessarily show up in the magnitude traces in SMAART.

For background when there are large PA systems that have been pushed hard for several years it is not uncommon for there to be many drivers in the overall system that while they produce "noise,"they do not perform to spec. As the system is so large, especially with line arrays, it can be harder to pin-point which exact enclosure or driver is having problems from a distance. Overall there is a feeling that "things don't quiet sound right." Not to mention that non-functional drivers can dramatically change the array behavior. Going through boxes individually with a sine wave can audibly reveal problems, but I would like a more scientific DUT process that gives actionably date in the form of a pass/fail to an enclosure, at which point the box can be dropped, taken apart, and drivers measured individually.

---
So for those of you who have dealt with "blown" or "tired" drivers what is your method of scientific verification?

I read on ASR that REW has a distortion test. If I utilized REW to perform a sine wave sweep, to calculate THD over frequency per box, would this be a good way determine if there are tired/blown drivers? Or are other ways that you would recommend?

---

I know many PA manufactures have ways of testing boxes and drivers via their amplification. Specifically the systems I will be working on are D&B and L'Acoustics (Load Monitoring for D&B and Enclosure Check for L'Acoustics). If I understand these respective systems would give information on individual driver impedance and whether or not they are functioning properly; however I am not certain I am setup to utilize these features as:
1) Install systems have some LONG cabling going in (I think these systems like less than 30ft between the amp and speaker)
2) None of the D&B systems have 1:1 box resolution.

Thanks in advance for the help, I am excited to learn and get my head around all of this! :)

Matthias
 
Last edited:

Philbo King

Addicted to Fun and Learning
Joined
May 30, 2022
Messages
669
Likes
874
I don't think at-distance measurements would work for all speaker faults. Nor for individual speaker faults that introduce distortion, especially in a large array.

You really need to address individual speaker enclosures one by one to do any sort of comprehensive tests.

One possibility might be dangling a mic from the top, pausing in front of each individual speaker for 5 seconds or so, while recording the mic input. That would indicate dead or distorting speakers. And if the test tone was known to start on, for example, a positive alternation, you could possibly detect speakers wired with backward polarity.

But generally it would be better to test these before they were flown in arrays. I know; time and logistics pressures might make that impossible...
 
OP
M

Matthias McCready

Active Member
Joined
Jul 2, 2021
Messages
209
Likes
273
Sorry if I did not explain more clearly, in my original post:

I will be measuring boxes individually, with the measurement mic placed at a distance of 3x the diagonal of the baffle, as recommended by the Trace-book project.

Where the process deviates, and hopefully not enough to mitigate the usefulness of the measurements, is that I will need to measure with the arrays/boxes still flown. I am hoping not to pull anything down unless problems are detected and further investigation is warranted.

----

To clarify some more:

1) These are installed PA's; and I am looking for a process to go through all boxes individually 1-2 times a year, without having to pull them down. Just to verify boxes are working according to spec, and performing as expected.
2) Every 3-5 years, or if problems are detected in the yearly verifications, the boxes will be taken down and measured according to the the Trace-book method.
3) As systems are replaced, or when new venues are added it is my intent to have everything measured before flown, both for the purposes of a "pre-flight" check, and as a reference for future measurements, ie what spec did this system perform to when new?

----

So the main questions I am still wondering are:

1) So for those of you who have dealt with "blown" or "tired" drivers what is your method of scientific verification?
2) Is a distortion sine wave sweep via REW an effective way to test individual enclosures for driver problems?

Thanks!

Matthias
 

Philbo King

Addicted to Fun and Learning
Joined
May 30, 2022
Messages
669
Likes
874
Ah, that clarifies a lot. Hmm ... Crazy idea - you might look into mounting an omni mic on a drone, and test each driver from very near field (like a foot or so) with a brief sine sweep. The sine sweep would allow freq gating so the drone noise would be a known blip on the sweep, while any other anomaly would point to a malfunction.
A malfunction that is level-sensitive is a rubbing voice coil - the quieter it is, the greater its distortion.
So level might be a variable too.
Automating the analysis would be desirable, as opposed to spending dozens of hours looking through plots... not sure where to go with that, however.
 
OP
M

Matthias McCready

Active Member
Joined
Jul 2, 2021
Messages
209
Likes
273
Ah, that clarifies a lot. Hmm ... Crazy idea - you might look into mounting an omni mic on a drone, and test each driver from very near field (like a foot or so) with a brief sine sweep. The sine sweep would allow freq gating so the drone noise would be a known blip on the sweep, while any other anomaly would point to a malfunction.
A malfunction that is level-sensitive is a rubbing voice coil - the quieter it is, the greater its distortion.
So level might be a variable too.
Automating the analysis would be desirable, as opposed to spending dozens of hours looking through plots... not sure where to go with that, however.

All of the venues have lifts, so getting to the boxes is not a problem; which is good as I am terrible drone pilot! ;)

Measuring locations for traces will be recorded and hopefully replicated year to year.
 
Top Bottom